The presently disclosed embodiments relate generally to layers that are useful in imaging apparatus members and components, for use in electrostatographic, including digital, apparatuses. More particularly, the embodiments pertain to a system and method for providing measurements of photoreceptor layer thicknesses. The present embodiments employ the use of dark field microscopy in combination with a noise reducing normalization technique to provide representative spectral responses for highly scattering pigmented layers that are generally difficult to obtain with conventional methods and require more equipment. As it was discovered that such spectral measurements can be correlated to photoreceptor electrical characteristics, the present embodiments are also used to provide real-time production adjustments to optimize photoreceptor characteristics and/or performance.
An electrophotographic imaging member may be provided in a number of forms. For example, the imaging member may be a homogeneous layer of a single material such as vitreous selenium or it may be a composite layer containing a photoconductor and another material. In addition, the imaging member may be layered. These layers can be in any order, and sometimes can be combined in a single or mixed layer.
Multilayered photoreceptors or imaging members can have at least two layers, and may include a substrate, a conductive layer, an optional charge blocking layer (sometimes referred to as an “undercoat layer”), an optional adhesive layer, a photogenerating layer (sometimes referred to as a “charge generation layer,” “charge generating layer,” or “charge generator layer”), a charge transport layer, an optional overcoating layer and, in some belt embodiments, an anticurl backing layer. In the multilayer configuration, the active layers of the photoreceptor are the charge generation layer (CGL) and the charge transport layer (CTL). Enhancement of charge transport across these layers provides better photoreceptor performance. Overcoat layers are commonly included to increase mechanical wear and scratch resistance.
The term “photoreceptor” or “photoconductor” is generally used interchangeably with the terms “imaging member.” The term “electrostatographic” includes “electrophotographic” and “xerographic.” The terms “charge transport molecule” are generally used interchangeably with the terms “hole transport molecule.”
The charge generation layer film is pigmented, and thus, conventional interference optics cannot be used to measure its thickness because a clear or translucent film would be needed to provide the required interference fringes. In addition, contact measurement devices do not provide the resolution needed to measure these sub-micron thick films. Because of this “gap” in measurement technology, current manufacturing processes of photoreceptor layers may result in inconsistent product performance. For example, some photoreceptors can exhibit high Vlow, reduced photosensitivity, and print defects. It was observed that these abnormal parameters can be correlated to the spectral reflection ratio of the films representative spectra. Conventional methods, however, require the coating of a full device, determining or checking the Vlow of the device, and subsequently feeding of the information back to the production line. As used herein, Vlow refers to the surface voltages of photoreceptor after light exposure, and “photosensitivity” refers to the surface voltage change rate to the exposure energy.
Thus, new and effective means to provide accurate and fast measurement of photoreceptor layers, especially those layers that are pigmented, are important to future enhancement of photoreceptor production and overall xerographic performance. In this regard, a measurement system that can provide real-time measurement and feedback of critical xerographic control parameters or variables during production will be highly desirable.